1. Field of the Invention
The present invention relates to a fire detector, and more particularly to a photoelectric type fire detector capable of photoelectrically detecting smoke generated as a result of a fire, as well as to a heat-photoelectric type fire detector which detects occurrence of fire by sensing both heat and smoke generated by the fire.
2. Description of the Related Art
In the conventional photoelectric smoke detector, when smoke arises due to fire, the light emitted from a smoke detecting light-emitting element of a light-emitting section is scattered by the smoke and enters a smoke detecting light-receiving element of a light-receiving section. The scattered light received by the light-receiving element is then amplified in an amplifying circuit and then sent to a fire discriminating section where fire discrimination is made on the basis of the output value. If it is determined that there is fire, the discriminating section transmits a fire signal to a fire signal transmitting section through an accumulating circuit, and the transmitting section sends this fire signal to a fire receiver etc. for reporting the fire.
In the conventional photoelectric type smoke detector, the sensitivity of the detector is adjusted by a sensitivity adjusting means and the operation of the fire discriminating section etc. is stabilized by means of a constant voltage circuit. Further, in such a type of detector, a pulse output of an oscillating circuit is supplied to an operation indicating lamp so that the lamp is intermittently turned on to indicate that the detector is normally operating.
In the conventional sensitivity adjustment, a reflecting plate, which would generate a scattering light being equivalent to the scattering light which would be generated when 10%/m of smoke has entered, is disposed in a smoke detecting dark box of the photoelectric type smoke detector, and a detected output at that time is used for selecting a reference resistance of a comparator as a fire discriminating means such that the comparator replies. As a result, the detected output would become varied due to the dispersion of the circuit constant of an electric circuit of the respective photoelectric smoke detector. This leads to troublesome procedure for the sensitivity adjustment i.e. the selection of the reference resistance. In addition, since a different value of the detected output is obtained in each of the photoelectric type smoke detectors, in order to know the historical variation of the sensitivity of the detector from the initial state, the initial detected outputs of the detectors must be recognized, which has been laborious procedures.
The conventional detector includes an accumulating circuit composed of a plurality of D-type flip-flops. Accordingly, for example, the fire signal would be sometimes undesirably transmitted from the fire signal transmitting section by the operation of the accumulating circuit upon turning on of the power source when the fire resetting operation is carried out.
The constant voltage circuit in the conventional detector is composed of a transistor, a Zener diode connected to a base of the transistor, and a resistor connected between a collector and the base of the transistor. Therefore, when there is a significant difference in the power source voltage to be supplied to the smoke detector between the fire receivers, the current to be consumed in the constant voltage circuit of the smoke detector varies depending on the fire receiver connected there to. For example, when the power source voltage is high, the current flowing through the Zener diode of the constant voltage circuit becomes correspondingly large, while when the power source voltage is low, the current flowing through the Zener diode of the constant voltage becomes correspondingly small.
Thus, in the case of a fire receiver with a high power source voltage to be supplied to the smoke detector, there is a disadvantage in that the number of smoke detectors which can be connected is significantly restricted due to the power consumption of the constant voltage circuit, in comparison with a fire receiver with a low power source voltage. Further, the power source voltage of the fire receiver is sometimes unstable and fluctuates. In such a case, if the fire detector is changed to a smoke detector having semiconductor circuits, a necessary number of fire detectors cannot be connected.
In the conventional detector, the oscillating circuit of the operation indicating lamp is provided separate from and independent of a pulse oscillating circuit for supplying the pulse output to the smoke detecting light-emitting element of the light-emitting section. As a result, even if the pulse oscillating circuit for detecting the smoke fails so as not to make the light-emitting element emit light i.e. in a fire monitoring disabled state, the indicating lamp flickers if the oscillating circuit is normally operable, erroneously indicating that the detector is in normal state.